Heretofore, it is know that discotic liquid-crystalline compounds are extremely important compounds for a material for optically-compensatory films, for example, a described in JP-A-8-50206. As a liquid-crystalline compound that expresses discotic liquid-crystallinity, disclosed is 2,3,6,7,10,11-hexa{4-(4-acryloyloxyhexyloxy)benzoyloxy}triphenylene (JP-A-7-306317). The liquid-crystalline compound is used in many optically-compensatory sheets heretofore know in the art.
On the other hand, the wavelength dispersiveness of optically-compensatory sheets must be controlled in accordance with the liquid-crystal display devices, as disclosed in JP-A-2004-184864. However, nothing has heretofore been reported, relating to liquid-crystalline compounds of which the wavelength dispersiveness is smaller than that of 2,3,6,7,10,11-hexa{4-(4-acryloyloxyhexyloxy)benzoyloxy}triphenylene (that is, those having a smaller value of Re (at short wavelength (e.g., 450 nm)/Re (at long wavelength (e.g., 650 nm)).
The retardation (Δnd) of optically-compensatory sheets must be determined depending on the optical properties of the liquid-crystal cells to be compensated by the sheet. The retardation (Δnd) as referred to herein is a product of the refractivity anisotropy (Δn) of an optically-anisotropic layer
and the thickness (d) of the optically-anisotropic layer. When the refractivity anisotropy (Δn) of an optically-anisotropic layer is large, then the liquid-crystal cell could be compensated even though the thickness (d) of the layer is thin. On the contrary, when the refractivity anisotropy (Δn) of an optically-anisotropic layer is small, then the thickness (d) of the layer must be large, and, as a result, there may often occur a defective problem in point of the alignment of liquid-crystalline compounds.
As a discotic liquid-crystalline compound having a large refractivity anisotropy (Δn) known is 2,3,6,7,10,11-hexa{4-(4-acryloyloxyhexyloxy)cinnamoyloxy}triphenylene as disclosed in JP-A-2001-166147. However, it has become obvious that the wavelength dispersiveness of this liquid-crystalline compound is larger than that of 2,3,6,7,10,11-hexa{4-(4-acryloyloxyhexyloxy)benzoyloxy}triphenylene.
Heterocyclic group-having tri-substituted benzenes are reported in Molecular Crystals and Liquid Crystals, 2001, Vol. 370, page 391. As a result of our studies, however, we, the present inventors have found that the compounds having that skeleton could not readily attain a lower wavelength dispersion than that of 2,3,6,7,10,11-hexa{4-alkyloxybenzoyloxy}triphenylene as so described in the Examples given hereinunder.
In consideration of the situation as above, an object of the invention is to provide a compound having a low wavelength dispersiveness that could not be realized by any conventional discotic liquid-crystalline compounds. Another object of the invention is to provide a liquid-crystalline compound capable of satisfying both low wavelength dispersiveness and high Δn. Still another object of the invention is to provide a composition containing the compound, and to provide a thin film formed by the use of the compound.